You are right, my question was not without a troubleshooting background.
In the past, I had a long term NFS troubleshooting with a network newbie as a communication partner. He was using the SG200-08P managed switch, but he didn't mention it. The network had been producing strange problems. NFS connections were not possible between the satellite receiver and the NAS. We spent ages trying out the settings on both the receiver and the NAS. In the end, I was able to convince him to install the latest (also end-of-life for several years) firmware, and voila - the error was gone.
I also know of some old changelogs for enterprise switches that had problems with DHCP relay. So maybe you should look for a changelog for the switch you are using and try to get a newer firmware.
Of course it could also be a problem on the kernel side, but I suspect the number of home users with managed switches is not very large, to get a valid feedback from others.
EDIT:
Depending on the switch vendor you use, "trunk" implies that all traffic at this port is tagged. That means, you must ensure that the client (RPi) know about it and configure the corresponding VLAN ID there too.